A U.S. appeals court has rejected a fourth request to move the trial for the accused Boston Marathon bomber to another city.

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(CNN) -- Defense attorneys representing accused Boston Marathon bomber Dzokhar Tsarnaev said in a Friday court filing the FBI asked his older brother, Tamerlan Tsarnaev, to be an FBI informant and report on the Chechen and Muslim communities in Boston.

"We base this on information from our client's family and other sources that the FBI made more than one visit to talk with (Tamerlan's parents) and Tamerlan, questioned Tamerlan about his internet searches, and asked him to be an informant," the defense motion states.

But the same court filing says the government denies the allegation and quotes a March 14 FBI statement that says, "[T]he government has no evidence that Tamerlan Tsarnaev was solicited by the government to be an informant."

Defense lawyers sought FBI documents to confirm their allegation and said it's possible "Tamerlan misinterpreted the visits and discussions with the FBI as pressure and that they amounted to a stressor that increased his paranoia and distress."

Dzokhar Tsarnaev is scheduled to be tried November 3. He is charged with 30 federal counts stemming from the April 15 bombing that left three people dead and more than 250 others injured. The attacks triggered the massive manhunt that led to Tsarnaev's capture.